1 Field of the Invention
The present invention relates to a solid-state imaging device suitable for use in an electronic still camera and so on, for example.
2. Description of the Related Art
In general, improvement of a resolution with respect to a letter, a figure or the like an electronic still camera is demanded.
A solid-state imaging device with an improved resolution in which color filters are arranged on a surface of an all-pixel reading solid-state imaging element in an arrangement of horizontal two pixel repetition x vertical two-pixel repetition has been proposed (Japanese laid-open patent publication No. 4-729899).
A solid-state imaging device in which color filters are arranged on a surface of the all-pixel reading solid-state imaging element in an arrangement of horizontal two pixel repetition x vertical two-pixel repetition can provide an effect of improving a resolution of xc2xd on a vertical spatial frequency when an aperture compensation signal is generated by using pixels for the same color in every vertical lines, as compared with a solid-state imaging device of an interlace scanning system.
Such conventional solid-state imaging device can provide the above effect only when pixels for the same color are arranged in a stripe fashion in a pixel arrangement of the color filter. However, in a color solid-state imaging device in which color filters having a checkered pixel arrangement that is not a stripe arrangement of the same color pixels are arranged on a surface of the all-pixel reading solid-state imaging device, if an aperture compensation signal is generated from signals obtained from the same color pixels, then resolution is improved by xc2xd on a horizontal spatial frequency and also by xc2xd on a vertical spatial frequency, but consequently a pseudo signal is disadvantageously generated.
The reason for generation of this pseudo signal is that since green pixels G of a color filter are arranged in a checkered pattern as shown in FIG. 1A and hence interpolation must be carried out in order to generate an aperture compensation signal, e.g., the aperture compensation signal must be generated after the interpolation is carried out with a horizontal-direction mean value of a green signal, if such horizontal-direction interpolation is carried out and an object has a horizontal stripe pattern with a spatial frequency of xc2xd as shown in FIG. 1B, then resolution can be carried out as shown in FIG. 1C, but if such horizontal-direction interpolation is carried out and an object has a vertical stripe pattern with a spatial frequency of xc2xd as shown in FIG. 1D, then a pseudo signal representing a horizontal stripe as shown in FIG. 1E is generated.
Contrary, if this interpolation is carried out with a vertical-direction mean value of the green signals, then if an object has a horizontal stripe pattern with a spatial frequency of xc2xd, then consequently an aperture compensation signal disadvantageously generates a pseudo signal representing a vertical stripe. As a result, the aperture compensation signal disadvantageously generates a pseudo contour at horizontal and vertical edges.
In view of such aspects, it is an object of the present invention to improve a resolution without generating a pseudo signal in a solid-state imaging device.
According to a first aspect of the present invention, a solid-state imaging device having a color filter of a checkered pattern arranged in an all-pixel reading solid-state image sensor includes an original signal aperture compensation means for forming an original signal aperture compensation signal from all pixels of a color filter, a luminance signal aperture compensation means for forming a luminance signal aperture compensation signal from a luminance signal obtained by synthesizing the all pixels of the color filter, and a chrominance signal ratio detecting means for detecting an output ratio of chrominance signals. The original signal aperture compensation signal and the luminance signal aperture compensation signal are weighed in response to a detection output from the chrominance signal ratio detecting means. Thereafter, the weighed original signal aperture compensation signal and the weighed luminance signal aperture compensation signal are added to obtain an aperture compensation signal.
According to a second aspect of the present invention, a color solid-state imaging device having a color filter of a checkered pattern arranged in an all-pixel reading solid-state image sensor includes an original signal aperture compensation means for forming an original signal aperture compensation signal from all pixels of a color filter, a chrominance signal detecting means for detecting whether an object is colored or colorless, and a storage means for previously storing a gain coefficient for aperture compensation. The gain coefficient of the storage means is read out in response to a chrominance signal detection signal from the chrominance signal detecting means and the original signal aperture compensation signal is weighed in response to the gain coefficient.